sears st16 transmission troubles

hello folks. ive recently bought a sears st16 with a johnson workhorse 10 loader. the tractor runs great, and the loader works. but it doesnt drive. there seems to be an internal issue that sometimes causes the drive pulley and the shaft to seize. the rear wheels turn. it goes into all gears in both ranges just fine with the engine off. the wheels spin, if you spin one forward the other turns backwards. does anyone have any idea what could be going on in the transmission. i was in the process of dropping the rear from the tractor when i realized the loader frame gets in the way of 2 bolts so i put that on hold for a few hours.

Welcome JPD. Is this a new problem or one you bought? Tractor sit outside?

I am not familiar with the inner workings of this transmission, but have been told they are practically bullet proof. I believe it is the same one as in my ST/10. That being said, I seem to remember they are known to get water inside and in winter it will freeze causing the trans to lock up. Try to warm up the machine and maybe change the fluid. Just a thought, I'm sure someone will be along to give you more information.

i bought this big cluster of a project. previous owner told me all it needed was the drive pulley welded on. seems to be alot more to it the further i dig. i figured it would be a nice machine to hold me over until my other loader project is done. i thought about the possibility of ice. i figured if it came down to that id drain the oil, which looks really new and clean, and put 5 quarts of a frost-kill, kero and seafoam mix into the trans and let it sit for a day. im just stumped for once.